In automotive cooling systems, water pumps are used to circulate liquid coolants between an internal combustion engine and a radiator to regulate the operating temperature of the internal combustion engine of the automobile. The water pump is typically driven by the rotational output of the internal combustion engine, for example, by a belt-driven pulley that is connected to a pumping mechanism of the water pump. Because work is performed by the internal combustion engine in order to drive the pumping mechanism of the water pump, operation of the water pump increases the rate of fuel consumption by the internal combustion engine.
When the temperature of the internal combustion engine is low, continuous operation of the water pump at full speed is not required to regulate the temperature of the engine. However, the belt or other means that drives the water pump typically remains in continuous motion during operation of the internal combustion engine, causing continuous operation of the water pump at full speed, regardless of engine temperature. Thus, it would be desirable to have an efficient mechanism by which the water pump could be disengaged or operated at a reduced speed in response to the temperature of the internal combustion engine.